The present invention relates to the production of display boxes for a variety of products. A large variety of boxes of this kind is known in which the actual display of the contents of the box is provided by means of a window formed by an aperture in the wall of the box covered by a transparent sheet of plastics material as a rule, which is applied to the interior of the box.
No problem of any kind arose if the window did not extend beyond one surface of the box and was limited in surface in such manner as not to overlap the edge folds.
On the other hand, for example in the case of a rectangular box, if it was wished to produce a window overlapping at least one edge fold, it was necessary in view of the presence of fold projections or the like on the cardboard panel, to make use of a thin and pliable sheet of plastics material. The result was that if the window had a considerable area, the box lacked stiffness and this raised problems for example whilst filling or handling the same.
Boxes of this kind which comprise windows extending across one or more edges of the box are known and, for example, described in the U.S. Pat. Nos. 3,292,513 and 3,273,702. In accordance with these two prior patents however, the windows are covered with sheets of a flexible or semi-rigid transparent plastics material.
In the U.S. Pat. No. 3,273,702, the box comprises a panel 2 of opaque cardboard which in known manner has incipient or preparatory fold lines 6a, 6b, 6c, 6d and 6e FIG. 3) delimiting the different sides 10, 12, 14, 16 and 18 of the box. The cardboard panel 2 has an opening 32 covered by a transparent sheet 4 which comprises fold lines 34 and excisions 36 situated in alignment with the extension parts or projections 38 of the cardboard panel. The sheet 4 of plastics material should be a semi-rigid sheet which is sufficiently flexible to be capable of being folded at a comparatively acute angle without a preparatory fold line or crease. The plastics material utilised in accordance with this patent are polystyrene, or bi-axially oriented PVC (column 3, lines 35 to 50). Furthermore, FIG. 2 clearly shows that the sheet 4 is actually a pliable sheet, allowing for the very founded off folding angles illustrated in particular in the upper part of the sheet 4.
The U.S. Pat. No. 3,292,513 discloses a box of a similar kind, in which the opening cut-out of a cardboard panel is covered with a plastics material sheet 28. In this case however, the form of excision of the opening which is comparatively complex and comprises reinforcing strips for the plastics material sheet, clearly demonstrates that the plastics material sheet should be a flexible sheet.
The boxes in accordance with these prior patents consequently lack stiffness which entails considerable trouble when it is required to store and handle them. Furthermore, they are unusable for packaging heavy elements such as bottles filled with a liquid. Finally, their production is complex and expensive as demonstrated in particular by the U.S. Pat. No. 3,292,513.